Excited-State Optically Detected Magnetic Resonance of Spin Defects in Hexagonal Boron Nitride
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-05-27 |
| Journal | Physical Review Letters |
| Authors | Zhao Mu, Hongbing Cai, Disheng Chen, Jonathan Kenny, Zhengzhi Jiang |
| Institutions | National University of Singapore, Nanyang Technological University |
| Citations | 56 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: Comprehensive characterization of the excited state (ES) spin properties of negatively charged boron vacancy (VB-) centers in hexagonal boron nitride (hBN) using Optically Detected Magnetic Resonance (ODMR).
- Zero-Field Splitting (ZFS): The ES longitudinal splitting (DES) was determined to be approximately 2160 MHz at 7 K and 2117 MHz at 293 K.
- Enhanced Contrast: A maximum ES-ODMR contrast of 12% was achieved at 7 K, significantly higher than the ~2% contrast observed at room temperature (290 K).
- Lifetime Correlation: The increased cryogenic ODMR contrast is attributed to the prolonged ES fluorescence lifetime, which extends from 0.67 ns (RT) to 2.32 ns (4 K).
- Level Anti-Crossing (LAC): The Excited-State Level Anti-Crossing (ESLAC) point was identified near 800 G (~2240 MHz), providing a critical magnetic field setting for future nuclear spin manipulation.
- Quantum Relevance: The results confirm the triplet nature of the ES and provide essential energy level information required for implementing Dynamic Nuclear Polarization (DNP) schemes in hBN spin defects, even at cryogenic temperatures.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spin Defect | VB- | N/A | Negatively charged Boron Vacancy |
| ES Zero-Field Splitting (DES) | ~2160 | MHz | Cryogenic temperature (7 K) |
| ES Zero-Field Splitting (DES) | ~2117 | MHz | Room temperature (293 K) |
| GS Zero-Field Splitting (DGS) | 3684 | MHz | Cryogenic temperature (7 K) |
| GS Zero-Field Splitting (DGS) | 3460 | MHz | Room temperature (RT) |
| Maximum ES-ODMR Contrast | 12 | % | Cryogenic temperature (7 K) |
| RT ES-ODMR Contrast | ~2 | % | Room temperature (290 K) |
| ES Lifetime (ÏES) | 2.32 | ns | Lowest temperature (4 K) |
| ES Lifetime (ÏES) | 0.67 | ns | Room temperature (RT) |
| ES g-factor | ~2 | N/A | Similar to GS g-factor |
| ESLAC Magnetic Field | ~800 | G | Corresponds to ~2240 MHz transition |
| GSLAC Magnetic Field | ~1330 | G | Ground state level anti-crossing |
| MW Stripline Width | 50 | ”m | Used for generating homogeneous in-plane B-field |
Key Methodologies
Section titled âKey Methodologiesâ- Sample Fabrication: A 50 ”m wide straight gold stripline was deposited onto a Si/SiO2 substrate to facilitate microwave (MW) delivery and generate a homogeneous in-plane magnetic field.
- hBN Integration: Exfoliated hBN flakes were transferred onto the gold stripline.
- Defect Creation: VB- centers were generated by bombarding the hBN with Ga+ ions at the center and edge of the gold line.
- CW ODMR Measurement: Continuous Wave (CW) ODMR spectra were acquired by cycling the MW power on and off (10 ”s duration each) while monitoring the photoluminescence (PL) intensity.
- Pulsed ODMR Confirmation: Pulsed ODMR sequences were used to confirm the ES nature of the 2351 MHz dip: a 5 ”s laser initialization, 500 ns dwell time, 1 ”s MW pulse, and 5 ”s laser readout.
- Two-MW Spectroscopy: An additional continuous MW (MW-2) was applied near the GS transition to induce spin mixing, confirming that the GS and ES signals originated from the same defect type.
- Level Anti-Crossing (LAC) Analysis: MW-free experiments were conducted by recording the PL emission intensity as a function of external magnetic field (B) applied nearly perpendicular to the hBN c-axis, identifying the ESLAC and GSLAC points.
- Temperature Dependence: Measurements of ODMR contrast and ES lifetime were performed across a range of temperatures (4 K to 297 K) to study the photodynamics and optimize contrast.
Commercial Applications
Section titled âCommercial Applicationsâ- Quantum Sensing and Metrology:
- Nanoscale Magnetic Field Sensing: Utilizing the VB- centers as 2D spin qubits for high-resolution magnetic field sensing, especially suitable for constructing van der Waals heterostructures for in-situ imaging of layered material properties.
- Temperature and Pressure Sensing: The spin defects can be employed as quantum sensors for measuring local temperature and pressure variations.
- Quantum Information Processing (QIP):
- 2D Spin Qubits: VB- in hBN provides a robust, optically addressable spin platform in a 2D material, ideal for integration into scalable quantum circuits and devices.
- Advanced Spin Manipulation:
- Dynamic Nuclear Polarization (DNP): The detailed knowledge of the ES energy levels and the identified ESLAC point are crucial for developing DNP protocols, which enhance the sensitivity of nuclear spin detection for advanced quantum applications.
- Cryogenic Quantum Technology:
- The high ODMR contrast retained at cryogenic temperatures (12% at 7 K) makes VB- defects suitable for quantum devices operating in low-temperature environments where high spin polarization is required.
View Original Abstract
Negatively charged boron vacancy (V_{B}^{-}) centers in hexagonal boron nitride (h-BN) are promising spin defects in a van der Waals crystal. Understanding the spin properties of the excited state (ES) is critical for realizing dynamic nuclear polarization. Here, we report zero-field splitting in the ES of D_{ES}=2160 MHz and its associated optically detected magnetic resonance (ODMR) contrast of 12% at cryogenic temperature. In contrast to nitrogen vacancy (NV^{-}) centers in diamond, the ODMR contrast of V_{B}^{-} centers is more prominent at cryotemperature than at room temperature. The ES has a g factor similar to the ground state. The ES photodynamics is further elucidated by measuring the level anticrossing of the V_{B}^{-} defects under varying external magnetic fields. Our results provide important information for utilizing the spin defects of h-BN in quantum technology.